In the ideal principle of gear transmission, if it is assumed that the two gears undergo pure rolling without any sliding at the pitch point and the gears themselves are regarded as rigid bodies, then theoretically, there should be no efficiency loss in gear transmission.
However, in the actual real situation, the materials used to manufacture gears can never reach the standard of rigid bodies. Due to material properties, elastic deformation inevitably exists. When gears constantly undergo this repeated elastic deformation during operation, energy will inevitably be consumed, resulting in efficiency loss.
In addition, the existence of elastic deformation causes the meshing of gears to no longer be the theoretically perfect pure rolling state, thereby generating sliding friction. This sliding friction not only increases energy consumption but also causes the generation of heat, further affecting the transmission efficiency.
Furthermore, the actual manufacturing accuracy is difficult to reach the absolute accuracy envisioned in theory anyway. This gap makes the actual meshing situation of gears significantly different from the theoretical model and unable to achieve pure rolling transmission.
At the same time, there is another factor that cannot be ignored, that is, the actual gear tooth surface is not as smooth and flat as imagined in the rigid body theory. The microscopic roughness of the tooth surface, tiny flaws, and traces left during the processing all have an impact on the actual meshing effect of the gears. These imperfections will increase frictional resistance, reduce the smoothness of the transmission, and ultimately lead to a reduction in mechanical efficiency.
To sum up, due to the combined effects of various factors such as the elastic deformation of materials, the limitation of manufacturing accuracy, and the actual conditions of the tooth surface, gears inevitably lose mechanical efficiency during the actual transmission process.